BEIJING—Wu Zhuan and Zong Yinghong don't wear wedding rings, nor do they hold hands or kiss in public. Instead, it is their matching turquoise shirts decorated with yellow and black hearts that signal that they are man and wife.

The newlyweds plan weekend outings—wearing matching gray hoodies, striped sweatshirts or a set of purple pig shirts—to window shop and gin up glances in places like Wangfujing, Beijing's version of Times Square.

"We want everyone to envy us," said Mr. Wu, a 32-year-old forestry and conservation consultant, sitting next to his identically dressed spouse.

Mr. Wu and Ms. Zong have stiff competition on their weekend jaunts. In a single hour on a recent Saturday afternoon, eight couples could be spotted walking down Beijing's hip shopping street Nanluoguxiang wearing either identical or matching outfits—black shirts with yellow hearts and smiley faces on them, or a skirt paired with a polo shirt of the same stripes.

One such couple, Jin Ying and He Yukun—wearing a blue-and-white-striped dress-shirt combo—said the first time they dressed alike was like a pledge to one another, an admission of feelings they hadn't fully expressed before.

In a country where matchmaking has traditionally meant little or no input from the young people involved, couples are wresting back control. As courtship gets redefined, one byproduct is a fashion trend that would make most high-end designers cringe.

A search for matching couple clothing—known as qing lü zhuang—on China's biggest e-commerce site Taobao, offers more than three million results from online stores that have launched to meet the high demand. In roughly the last year, searches for the clothing have increased by 57%, according to Alibaba Group, Taobao's parent.

The phenomenon has its versions in the West—say, portraits of families sporting matching Christmas sweaters. A move toward his and her clothing failed years ago. In China, though, the trend provides a framework for romance, something that hasn't always been the primary factor in a relationship.

For hundreds of years, parents and grandparents parsed out family trees, calculated dowries and read astrology charts to arrange marriages. And even in recent years, many matches have sprung from a plan for a better material life, the promise that a combined income could afford a new home and maybe even a BMW.

Ms. Zong, a 31-year-old accountant in Beijing, said she chose to marry Mr. Wu, whom she first met in 2007, because he makes her laugh. Mr. Wu said it was Ms. Zong's gentle nature that won him over. "I would call her just to hear her voice," he said.

ENLARGE

Jin Ying, He Yukun

Ms. Zong says her parents, farmers who grow corn and beans in China's northeastern Jilin province, sometimes wear similar colors—gray and black—and old Mao-inspired jackets from years past, though that is less an expression of affection than an old remnant. She could never imagine them deliberately wearing matching shirts as symbols of love, she said.

"The first time they met was on their wedding day," Ms. Zong said. "Surely they love one another, but our love is different," she said.

For Mr. Wu and Ms. Zong, their coordinated-fashion debut wasn't long after they started dating. "It made us official," said Mr. Wu.

Sun Peidong, an associate professor at Shanghai's Fudan University, says the phenomenon reflects an increasingly materialistic society that is obsessed with logos and labels. People want BMWs to show they are rich; now they want matching-couples labeling to show they are in relationships, said Ms. Sun. And ultimately, matching duds is a way for people to feel secure, she said.

Bai Zhengping, just six months into a relationship, asked his girlfriend Ma Xin to accompany him on a shopping trip to buy twin Superman shirts. "I felt proud, like I was saying, 'She's mine,' " said Mr. Bai. "I just wanted everyone to know," he said, noting they have been together now for two years. She smiled and said, "I was so happy he asked."

Clothing designer Zhou Yougen launched online in 2011 his couples label Fei Chen, whose tagline says, "Listen to the heart, the beating of one another." He said the fashion category has evolved from mere matching T-shirts to trendy dresses and shirts that complement one another. Best-sellers like a yellow and blue cotton dress with accompanying boyfriend knit shirt helped Mr. Zhou's 2012 revenue reach 800,000 yuan, roughly $130,000, increasing 15 times from a year earlier, he said.

Mr. Zhou, who is 40 and sometimes pairs his outfits with his wife's, said the segment has so much potential that he is toying with the idea of designing more mature outfits for older couples, or for entire families.

Couples have the option of buying identical shirt sets or outfits that play off one another. For example, on the couples section of the site Wholesale7.net, "Spring Lovers" shirts feature two separate heart halves and a disjointed message that is only readable when seen as a set: "Let Love…Create Miracle." The company says sales of its matching couple shirts jumped 30% last year.

Major brands have taken notice, pushing the fashion statement to new levels with his-and-hers underwear. PVH Corp., parent of Calvin Klein, creates sets sold especially for Asia. Calvin Klein also stocks matching pajamas in China.

Not everyone is immediately won over by the trend. Zhi Yingli, a 21-year-old student in Beijing, said she was mortified when her ex-boyfriend wanted them to flaunt identical clothes. "It's like you're parading your most private feelings," she said. After some months, it grew on her, she said.

But since they broke up, Ms. Zhi won't wear any of the half-set of the clothes she still has in her closet. "Maybe only if I haven't done laundry for weeks," she said.

Meanwhile, Mr. Wu and Ms. Zong say they hope to be dressing alike for years to come and plan to expand their matching wardrobes. Ms. Zong said they are preparing for winter and are even considering buying special mittens, consisting of one mitten for him and one for her and a muff in the middle so the couple can stay warm without ever having to let go of each other's hands.

I guess it's cute... but this is still stupid. It reminds me of people trying to mark their territory. If you lack that much confidence in your relationship that you're compelled to stick it out on display and show the rest of the world, or if you feel the need to try and "mark" your other half, perhaps you're in a relationship for the wrong reasons.

I'd be more worried about focusing on how to be a good boyfriend/girlfriend or how to actually sustain a relationship than I would be about how "cute" we looked matching together. But maybe that's just me.

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